kdb: Use str_plural() to fix Coccinelle warning

Fixes the following Coccinelle/coccicheck warning reported by
string_choices.cocci:

	opportunity for str_plural(days)

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240328140015.388654-3-thorsten.blum@toblux.com
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

Author: toblux

kernel/debug/kdb/kdb_main.c

@@ -2517,7 +2517,7 @@ static int kdb_summary(int argc, const char **argv)
 	if (val.uptime > (24*60*60)) {
 		int days = val.uptime / (24*60*60);
 		val.uptime %= (24*60*60);
-		kdb_printf("%d day%s ", days, days == 1 ? "" : "s");
+		kdb_printf("%d day%s ", days, str_plural(days));
 	}
 	kdb_printf("%02ld:%02ld\n", val.uptime/(60*60), (val.uptime/60)%60);